Conservative MP Andrew Tyrie, chair of the Treasury Select Committee, has expressed concern over the way the Royal Bank of Scotland and Lloyds have restricted some of their customers from using cash machines owned by rival banks.

One million basic account holders with RBS will soon be barred from withdrawing money from the ATMs of other high-street retail banks. Lloyds have had a similar policy in place for a number of years.

In a strongly worded letter to the chiefs of RBS and Lloyds, Tyrie said he believed the practice had "major implications for access to universal banking customers and appears to target vulnerable customers who are most at risk of financial exclusion."

In response, Brian Hartzer, the head of RBS's retail operation in the UK, said that his bank could not afford to pay the charges incurred every time an RBS customer checked their balance or made a withdrawal at a rival cash machine. He also pointed out that that RBS customers would still have access to machines at NatWest, the Post Office, and supermarkets Tesco and Morrisons.

RBS and Lloyds are both partly owned by the British tax payer.